1. Field of the Invention
The present invention relates to a method for forming a color layer for use in a color filter, etc., and, in particular, the present invention relates to a method for forming a color layer, which includes a plurality of colored resists, on a substrate.
2. Description of the Related Art
One of important conditions required in a colored resist hardening step in a fabrication method for forming an optical color filter used in a flat display panel such as a plasma display panel or in a camera, etc., is that the colored resist hardening step does not cause defect or abnormality in a resist pattern to be formed in a later step.
A conventional procedure for forming a color filter on a substrate will be described with reference to FIG. 6.
After a pre-cleaning step to be performed in order to wash away extraneous substances adhered to the substrate (step S31, step S38, step S45), a resist coating step (step S32, step S39, step S46) for coating the substrate with a light-sensitive colored resist is performed. Thereafter, a drying step (step S33, step S40, step S47) under reduced-pressure for evaporating and removing solvent contained in the resist and a temporary baking step (step S34, step S41, step S48) are performed. Subsequent to the temporary baking step, an exposing step (step S35, step S42, step S49) for printing a pattern in the resist is performed and then a developing step (step S36, step S43, step S50) for developing the printed pattern is performed. Thereafter, a normal baking step (step S37, step S44, step S51) for sufficiently heating the developed pattern formed on the substrate to completely evaporate solvent contained in the resist and thermally harden the patterned resist by a hotplate or an oven is performed. The above series of the steps is performed every time when each of the first, second and third primary colored filter patterns is formed.
However, in the above mentioned fabrication procedure, the normal baking is performed at a temperature of 200˜230° C. for about 1 hour. Therefore, considering a time for heating the substrate up to the baking temperature and a time for cooling the substrate, a required time in the normal baking step becomes 3˜4 hours, which is the longest time in the color filter fabrication procedure. Therefore, there is a problem in view of improvement of producibility of color filter.
In order to solve this problem, JPH11-337724A, for example, discloses a technique in which the hardening step of the resist is performed in a temporary post-baking step under a generous condition compared with the condition of the normal baking step.
According to the technique disclosed in JPH11-337724A, a temporary post-baking step, that is, a half-hardening step, for thermally hardening the resist pattern to a hardness level, in which the resist pattern is not peeled off in the succeeding developing step, is used in lieu of the normal baking step for complete hardening the resist under the above mentioned condition for every color layer. However, after the last color layer of three primary color layers is patterned, the normal baking of the three color layers is performed at one time. Thus, the disclosed method is effective in reducing a time required for the resist hardening step of the color layer forming method including the pattern formation by coating the substrate with the resist on the substrate and repeating the pattern formation for the primary colors.
However, a further reduction of time required for the color layer forming method is requested. It may be thought that further reduction of the required time is possible by not further reducing a time required for the temporary post-baking step but slightly increasing the temperature of the temporary post-baking step. However, according to experiments conducted by the present inventors, it has been found that the surface hardness of the color layer resist becomes insufficient and developing agent in the subsequent step soaks into the color layer.